Anchoring device of steel wire for prestressed concrete



April 22,` 1969' MOTQHMQ SUZUK| ET AL 3,439,462

ANCHORING DEVICE OF STEEL WIRE FOR PRESTRESSED CONCRETE Filed Nov. 1'?. 196e sNvENTcRS Mover-"ko suzuki osAMu KoHRIYAMA' KAzum AovAMA @,Sbmm {wi AT1-eeuws sheet of?.l

MOToHlKo suzuKl ET AL 3,439,462 ANCHORING DVICE OF STEEL WIRE FOR PRESTRESSED CONCRETE April 22, 1969 Filed Nov. 1T. 1966 MIENTES mm uA WY S..2 H oo wk H OU vm AVS Mo KAZUMI YMA ZENZABUOU TAKUMA lcwm,` S/dman nTToRNEYs United States Patent O U.S. Cl. 52-223 2 Claims ABSTRACT OF THE DISCLGSURE An anchoring device for prestressed concrete which comprises a plurality of steel wires, each having a head at the ends formed in a generally rectangular shape in crosssection, the shorter dimension of which is substantially equal to the diameter of the wire and the longer dimension of which is approximately twice the diameter of the wire, the neck of the head is formed a tapered portion whereby it is not susceptible to cracks, an annular anchor having a plurality of slots cut in a radial direction, the length in the radial direction is an integral number times the shorter dimension of the head whereby multiple wires are inserted in the slot, adjacent longer sides of the head are in close contact thus there is no risk of the wires turning in either direction around the longitudinal axis of the w1re.

This invention relates to an improved anchoring device of steel wire for prestressed concrete aiming to provide prestress to concrete when structures in general including bridges and buildings are to be constructed with concrete.

This steel wire for prestressed concrete is of a diameter usually mm-10mm., and is hereinafter referred to simply as steel wire.

The purpose of this invention is to provide enough rigidity to steel wire so that when such wire is subjected to strong outer force, its heads formed in both ends might not be injured thereby.

Another purpose of the present invention is to provide a secure engagement of the head of steel wire to the anchor by forming such head of steel wire in a rectangular shape, the length of which is dimensioned suciently longer than the diameter of steel wire.

Still another purpose of this invention is to avoid cracks being produced in the head, in spite of it being made possible in so large by cold working in yboth ends of steel Wire.

One more purpose of the present invention is such that even after the heads have been formed in both ends of steel wire, such steel wire may be removed from anchor, thus the cold working of heads is easily performed and whenever steel wire is cut by an extraodinary outer force, such steel Wire may be replaced with new one Without any trouble.

Still one more purpose of the present invention is Such that when the head portion of steel wire engages anchor, said head will not lbe angularly displaced and yet for this prevention of angular displacement, there is no need to employ any particular additional parts.

The feature of anchoring device in the present invention resides in that the cross section of the head formed at both ends of steel wire is made rectangular whose endwise dimension is approximately same to the diameter of steel wire and whose lengthwise dimension is approximately two times the diameter of a steel wire and this head is tapered in its neck portion.

Another feature of this invention is such that the anchor holding the head of steel wire is annularly shaped with a plurality of slots extending in a radial direction, such Slots are cut to form a tapered vface on both sides so to snugly t the necked portion of the head and said anchor is exteriorly threaded to engage a pipe of thick wall and its inner face is also threaded to engage a pulling rod.

The characteristics of this invention will be more apparent as description proceeds with reference to accompanying drawings.

FIG. 1 is a side View of a part of steel wire for prestressed concrete of the conventional anchoring device.

FIG. 2 is a plan View of the above steel wire.

FIG. 3 is a plan view of anchor to secure steel wire shown in FIG. 1.

FIG. 4 is a section view taken along the line IV-IV in FIG. 3.

FIG. 5 is a side View of a part of steel wire that was invented by the inventors Ibefore the present invention is made.

FIG. 6 is a plan view of steel wire shown in FIG. 5.

FIG. 7 is a plan view of anchor `for anchoring steel wire shown in FIG. 5.

FIG. 8 is a cross section taken along line VIII-VIII shown in FIG. 7.

FIG. 9 is a side view of steel wire in the present invention.

FIG. 10 is a plan view of stel wire shown in FIG. 9.

FIG. l1 is a plan view of anchor which secures steel wire in the present invention.

FIG. 12 is a cross section taken along the line XII-XII shown in FIG. 1l.

FIG. 13 is a section of anchoring device of the present invention showing a status put in use.

FIG. 14 is a part of FIG. 13 showing its particulars.

FIG. 15 shows another status than that shown in FIG. 14.

In FIG. l, there is shown a conventional steel wire 1 having a head 2 shaped as nailhead. In forming this head 2 of nailhead shape at the end of steel wire, the portion of wire 1 is inserted into the perforated hole of an anchor 3, as seen in FIG. 3 and FIG. 4 and as it is, force is applied to the end of the steel wire in a direction shown by arrow A1, thus it is projectingly expanded in a radial direction.

This working is made in most cases by cold working.

Now let the diameter of steel wire 1 be do and the diameter of head thus made by cold working be d1, then an enlarged ratio of the head `will be represented as dldo wherein the larger the diameter the better stability of engagement, head 2 to anchor, will be obtained. According to experiments, it is said the best enlargement ratio of such head is to be approximately 1.5-1.6 times the diameter of steel wire.

The reason why this value of enlargement ratio be most suitable is such that if the ratio exceeds 1.6, a great many cracks 2c will get a rise over all the periphery of the head 2 in an axial direction of steel wire and in the other hand if the ratio is less than 1.5 the stability will be reduced when the head 2 engages the anchor 3 as seen in FIG. 3 and FIG. 4 because of too narrow engaging portion of the head. Also as to the reason why cracks 2 come out, it is deemed that this is due to the matter that at the abutment 2 of steel wire 1 to head 2, the parallelty of fibrous direction in steel wire 1 is subjected to a sudden change and as a consequence the rigidity of this head portion is greatly reduced.

In the next, the head 5 of steel wire 4 shown in FIG. 5 and FIG. 6 is formed in a shape of a fan by applying force from the sides of wire in a direction shown by arrow A5.

The anchor 6 to hold steel wire is of a ring shape, as seen in FIG. 7 and FIG. 8. In this ring shape anchor, a number of perforated slots 7 are provided in a radial direction.

Each slot 7 is perforated in a taper 8 so that the neck portion 5 of said head 5 may fit snugly thereto. 9 is a wedge. 10 is a pipe of thick wall to which the outer peripheral surface of anchor 6 is threadedly engaged.

Now let the diameter of steel wire 4 be d0 and the length of the top surface of the head 5 be d5. In this instance the enlargement ratio t5/d2, approximately 1.5- 1.6 is found to be most suitable according to experiments.

In this instance, as the width d5 of the top surface of the head 5 comes to be narrower than the diameter do of steel wire 4, when a plurality of such steel wire are inserted in the slot 7 of anchor 6, these wires contact to one another tending to turn in a direction shown by arrow A5 in the slot 7 as is referred to in FIG. 7. Such turn causes the neck portion 5 to displace relative to the bearing taper proportion 19 whereby the engagement thereto becomes unstable. In order that the steel wires might not turn, it is necessary to secure steel wires 4 to anchor 6 by the insertion of wedges 9.

According to the present invention, the head 12 of steel wire 11 as an anchoring device is formed in a rectangular shape in its top surface as well as in its cross section as seen in lFIGS. 9 and 10, the length d12 of the short side S12 being equal to the diameter d0 of steel wire 11 and the length d12 of the long side L12 of the rectangular being larger than the diameter do of steel wire 11. The enlargement ratio i12/d0 of the head 12 in this instance may be made approximately two times. This far exceeds the aforesaid enlargement ratio 1.6 in the conventional head, yet none of the cracks comes out in the head. 12 represents a taper formed in the neck of head 12.

As the enlargement ratio in length can be thus increased up to two times, when the head engages the anchor, respective ends of head extend over the surface of anchor as -far as 1/2 the diameter of steel wire whereby the head may easily and securely rest on the anchor as seen in FIG. 11. This permits the length of head engaging the anchor to be not necessarily strictly precise, that is, a larger permissible error in engaging portion may be granted in forming heads, thus man hour in manufacturing the anchoring device will be greatly economized.

The status of applying this anchoring device to structures is shown in FIG. 11FIG. 13. In FIG. 13, number 13 represents a part of the structure. 14 is an anchor plate, 15 a sheath. 16' indicates an end sheath, the diameter of which is larger than that of aforesaid sheath 15. 17 is an anchor to which steel wires are inserted. This status is shown more particularly in FIG. ll and FIG. 12. Therein 18 are a plurality of slots cut in a radial direction in anchor. The both sides of respective slots are formed in a tapered face 19. The outer end of respective slots 18 is opened and the length in radial direction is integer number times the diameter do of steel wire.

In inserting steel wire with head 12 to slot 18, wire is inserted from the periphery of anchor 17 toward the center thereof in a manner that the direction of the longer side L12 of head comes to be right angle to the radial direction of anchor 17 and the tapered portion 12 of head 12 is set to the tapered face 19 of slot 18. There is shown in FIG. 1l a status that two steel wires are inserted in one slot 18 of anchor.

After steel wires 11 have been placed in all of the slots 18, a pipe 20 of thick wall is threadedly engaged to the periphery of anchor 17 whereby the open end of respective slots is closed thus steel wires 11 are constrained in respective slots 18 of anchor 17 from being moved toward radial direction.

In the next, a pulling rod 16 is threaded into the inside of pipe 20 as seen in FIG 14, then said rod 16 is pulled with a jack (not shown) in a direction shown by arrow A16 whereby stress is given to steel wires 11 and the length of steel wire is substantially stretched.

Under this condition, a nut 21 is threaded to the exterior of the pipe 20 keeping tension as seen in FIG. l5. Rod 16 is removed after then.

According to the present invention, hence the steel wires 11 having head 12 formed in both ends are enabled to be inserted in anchor 17 even in the status that wires are housed in sheath 15 and end sheath 16', the operation of forming heads 12 may be made apart from the sheath 16. Also when steel wire is cut by accident, such wire may be taken out of sheath 15 and end sheath 16 thus other steel wire 11 may be replaced with very easy operation.

Contrary to this, in the anchoring device as referred to in FIG. 1 to FIG. 4 the work of making head is usually made in workshop rather than on the spot of construction, so that all the materials of steel wire 1 with head yet housed in sheath 15 and end-sheath 16 should be carried as they are to that very spot of construction, thus extreme difficulty is found in that troublesome transportation.

Further hence steel wires 1 with anchor 3 can not be passed through already finished structure, if any of wires or all of wires are cut by accident in tension work, such wires can not be replaced with new ones whereupon the structure may often result in out of use.

Still further hence the head 12 in the present invention has a tapered portion 12', there will get no cracks thus the rigidity of this portion is greatly increased.

In addition to this, the head 12 of the present invention is so shaped that the length of its shorter side S12 is same with the diameter d0 of steel 11 wire and the longer side is integer number times the diameter do of steel wire 11, when desired numbers of steel wire 11 are placed in the slot 18 and all are tightened by a pipe 20, see FIG. 11, adjacent longer sides L12 of head contact closely to one another wherein there will be no fear that respective wires might turn in either direction around the axis of respective steel wires. This is contrasted to that shown in FIG. 7 whose anchoring effect of wires are greatly reduced.

What is claimed is:

1. An anchoring device for prestressed concrete comprising a plurality of steel wires, each having a head at the ends formed of a generally rectangular shape in crosssection, the shorter dimension of which is substantially equal to the diameter of the wire and the longer dimension of which is approximately twice the diameter of the wire, the neck of said head having a tapered portion, merging with the wire, an annular anchor having a plurality of slots cut in a radial direction, the length of which is an integer number of times the shorter dimension of 5 the rectangular head, and the width of which is substantially the diameter of the wire, both sides of said slots on the outer surface of said anchor being formed in a tapered face snugly receiving the head tapered portions of a plurality of Wire heads nested in said slots side by side; and a thick walled tube threadedly engaged over the periphery of said anchor closing the open ends of the respective slots.

2. An anchoring device as set forth in claim 1, in which said tube is interiorly threaded adapted to engage a pulling rod and also is exteriorly threaded adapted to engage a securing nut.

References Cited UNITED STATES PATENTS 1/1959 Brandt 52-223 XL 6/1961 Guit 52-223 XL 3/1967 Kourkene 52-230 4/ 1967 Macchi 52-230 U.S. Cl. X.R. 

